1. Field of the Invention
The present invention relates generally to devices utilizing heat filters and condenser lenses and, in particular, to projection aparatii and similar devices.
2. Description of the Prior Art
It is a common experience of 35 mm projection slide viewing to have watched a valuable yet fragile slide crinkle up in the projection gate because a broken heat filter was not replaced before the projector was used again. This experience is not limited to 35 mm slide projectors but occurs in other projection type devices utilizing a separate heat filter.
U.S. Pat. No. 4,850,685 (col. 3, lns. 65-68) refers to a separate condenser lens and a heat filter that are combined in light source member module (i.e. housing). This approach does not solve the broken heat filter problem.
U.S. Pat. No. 3,953,730 also refers to a condenser which contains a heat filter 190. However, the condenser lens elements are separated from the heat filter even though they are located in the same xe2x80x9ccondenser module.xe2x80x9d
It is an object of the present invention to provide efficient means for projection viewing, and in particular projection slide viewing, that would prevent a heat-related breakup of a heat filter in projection type devices.
It is also an object of the present invention to provide a single optical component capable of serving both as a condenser lens element and as a heat absorption filter.
These and other objects are achieved by a heat absorptive optical component having a front surface and a rear surface where one of the surfaces is a crenulate surface having optical power.
According to one embodiment of the present invention, the crenulate surface is a diffractive surface.
According to another embodiment, it is a Fresnel surface.
It is also an object of the present invention to provide a projector apparatus comprising an integral condenser lens element and heat filter.
The crenulate surface serves two purposes. First, it permits design of a condenser lens with a uniform or near uniform thickness and therefore, uniform heat absorption. Second, it provides much more surface area than a plano or spherical surface to re-radiate or otherwise dissipate the heat. This latter feature greatly reduces the tendency of the element to break.
An additional advantage of the invention is the reduction in the number of optical components required in an assembly of the projector-type devices with a corresponding reduction in parts costs as well as assembly costs and the increased quality of such devices (no prize slides fried before an audience).